This invention relates to an improved clipper for attachment of U-shaped clips about gathered material and more particularly to the crimping die associated with such a clipper.
Metal U-shaped clips of the type including a crown and depending legs are often used to close or seal packages by being formed about gathered package material such as plastic netting or plastic wrapping material. The apparatus for attaching such clips about gathered material includes a punch which is driven in a channel against the crown of a clip in the channel. The clip thus moves down the channel into engagement with a die that forms the legs of the clip about the gathered material. Typical of prior art patents illustrating such a mechanism is U.S. Pat. No. Re. 30,196 for a "Single Piston Operated Clip Device" in the name of Velarde reissued Jan. 22, 1980, which patent is incorporated herewith by reference. Another device which applies to clips about a single portion of gathered material is depicted in U.S. Pat. No. 4,001,926 issued Jan. 8, 1977 entitled "Double Clipper, Single Piston Operated Device" in the name of Velarde.
It is often desirable to apply two clips, side by side and simultaneously, to a single portion of gathered material. In the past, when two clips are applied simultaneously, a problem has been encountered because the material being clipped may have non-uniform or unequal cross sections. For example, one of the two clips may also encircle a fastening strap.
Because the adjacent portions of gathered material may have unequal cross sections, one clip will be more loose than the other clip. This occurs even though the length and stroke of the punch and position of the die with respect to both clips is identical. In order to compensate for this discrepancy, punches of various lengths have been installed to act on adjacent clips. This requires manufacture of punches of various lengths and appropriate installation of the punches in the clipper apparatus. For this reason, the cross section of the gathered material differs for the adjacent clips.
As an alternative to use of punches of various lengths, adjacent shims have been inserted beneath the adjacent dies. The shims are small plates inserted under a die to adjust the die to the correct position for the clipping operation. This usually requires assembly and disassembly of the clipper in order to locate the shim. This is very time consuming and costly and may not produce the required adjustment except after many trial and error efforts.
The present invention contemplates a construction which overcomes the problems noted with respect to closing a clip with a cooperative punch and die.